凝固参数对定向凝固合金DZ22枝晶特性的影响

Improvement of Dendritic Characteristics of Superalloy DZ22 Directionally Solidified with Superhigh Temperature Gradient

采用ＺＭＬＭＣ超高梯度定向凝固装置，研究了不同凝固参数下定向凝固高温合金ＤＺ２２的枝晶特性．结果表明，冷却速率增大，枝晶臂间距显著细化，枝晶偏析被强烈抑制．当冷却速率为５４．２Ｋ·ｓ－１时，一次、二次枝晶臂间距λ１和λ２分别为２８．μｍ和８．４μｍ，Ｎｂ、Ｔｉ、Ａｌ、Ｃｒ、Ｃｏ。

Research work, mainly concerned with improvement of mechanical propertics of superalloys with superhigh temperature gradient, bas been steadily undertaken at Northwestern Polytechnical University (NPU) for some six years. This research requires special equipment ZMLMC (Zone Melting and Liquid Metal Cooling) which was especially designed by NPU Department of Materials Science and Engineering. With ZMLMC equipment, a superhigh temperature gradient of 1300K cm-1 can be reached. NPU bas done research on dendritic characteristics, under superbigh temperature gradient, of Al-4.5%Cul[1], cobalt-base supcralloy[2] , and nickel-base supcralloy[3]. In this paper, the authors present their rescarch results on such dcndritic charactistics of supcralloy DZ22 (approximately equivalent to the well-known U .S. DS superalloy PWA1422). When cooling rate is raised, the dendritic arm spacings of DZ22 become significantly smaller and the dendritic segregation is strongly suppressed. When cooling rate is 54.2K s-1, the primary and secondary arm spacings Al and 2 arc respectively about 28.8μm and 8.4μm, the segregation ratio of clements Nb, Ti, Al, Cr, Co and W all approach unity very closely.